A solid state disk (SSD) is a high performance storage device that employs non-volatile flash memory such as NAND and contains no moving parts. SSDs are much faster than typical hard disk drives (HDD) with conventional rotating magnetic media. A controller in the SSD manages operations of the SSD, including data storage and access as well as communication between the SSD and a host device. Since SSDs employ NAND memory components instead of rotating magnetic platters, physical constraints of data retention and recording accuracy differ. Due to the differences in the physical media NAND memory components, as well as the speed and performance differences, error correction mechanisms such as parity functions accommodate these physical media characteristics.
SSDs are typically made up of a number of NAND packages, each with 1-8 NAND dies per package, with each die made of multiple planes, blocks and finally pages. Another peculiarity with NAND is that NAND may only be written at the page level. In modern drives that may dictate a granularity of 8 KB, 16 KB or even 32 KB. A further characteristic of granularity is that NANDs may only be erased at the block level, which for a typical 25 nm NAND is 256 pages (2048 KB).